A vessel cover known from DE-OS No. 27 45 622 consists of an outer and an inner ring which are solidly connected with each other by means of supports. Freely exposed cooling coils are provided between the two rings on the side which faces the furnace hearth and are mounted on the rings by means of mounting brackets. The cooling-pipe coil consists of U-shaped winding pipes which lie closely against each other and are connected with each other through welding. The cooling-pipe coil is connected to a supply pipe through which the cooling water is fed under elevated pressure into the outer-most turn of the coil. The exit for the cooling water is provided at the inner turn of the cooling-pipe coil. The space between the inner ring and the electrodes is filled out with a refractory lining which is customarily arranged around the electrodes.
Experience has shown that when this vessel cover is used, material difficulties ensue in handling the cover during maintenance work because the entire cover has to be removed from the furnace vessel after switching off the cooling-water connections. In case of repairs at the infeed or the individual cooling elements, extensive dismantling has been necessary because the cover is erected as a compact unit. Besides, a complete replacement cover had to be available.
It is therefore the object of the present invention to build a vessel cover, of the general type mentioned above, which does not have the enumerated disadvantages, but one which is designed in such a way that the inner lined cover center or the cooling unit may, if necessary, be constructed separately.
This object is achieved according to the invention through the features of the cooling pipe coil which is connected to the cover frame and lies exposed toward the furnace hearth, which when viewed from the top leaves an area open above the center of the container cover, and is formed as a self-supporting unit; the outer cover frame is connected with a frame from which it may be released; the frame is arranged above the cooling coil in a plane extending parallel to the cover frame and is connectable to a hoisting unit for the arc furnace cover; the refraction-lined center is arranged at the frame and is suspended and detachable in a manner whereby the outer circumference of the cover center fits onto the inner circumference of the cooling coil.
Thus, in accordance with the invention, maintenance work is materially facilitated, thereby reducing operating costs. In this regard the arrangement of a sub-frame is essential, to which subframe are mounted, independently of each other, the self-supporting cooling-pipe coil and the lined cover center.
For repair work at the cover in-feed, the connection between the subframe and the cover hoist unit is released and the lined cover center is lifted off, without the subframe, with the help of a crane, by connecting the loading means of the crane to the bent support arm of the cover center. The cover center can be set aside on the repair stand.
In this manner, the cooling-pipe coil, which is connected to the cooling circuit, rests on the furnace vessel. During repair a replacement cover center may be brought above the furnace vessel and may be connected with both the subframe, which rests against the vessel, and the cooled cover element.
Should there be repair work required at the cooling unit, the lined cover center with its ring-shaped frame may be swivelled away so as to make possible repairs to the cooling coils at the furnace or at a repair stand.
Finally, it is possible to lift the complete furnace cover together with subframe off the furnace vessel.